1. Field of the Invention
This invention relates to solid adhesives of stick type having readhesion properties and more particularly to stick adhesives having readhesion properties which enable sheets to be removably adhered to an adherend in such a cyclic manner as adhesion-removal-readhesion.
2. Prior Art
There have been provided liquid adhesives containing organic solvents, which enable sheets to be removably adhered to an adherend. For example, they have been used when printing art works are made.
On the other hand, solid adhesives of lip stick type have been provided, for example by Muszik et al as shown in the Japanese patent publication No. 47-25448 and the corresponding U.S. Pat. No. 3,576,776, which comprise adhesive substances which are soluble or dispersible in a liquid medium such as water, water-miscible organic solvents or aqueous solution thereof and alkali metal salts or ammonium salts of aliphatic carboxylic acids as a gelatinizer.
The above liquid adhesives, however, have such drawbacks as environmental pollution caused by the volatilization of organic solvents which induces sanitary problems, fire risk and so forth.
Solid adhesives mentioned above do not possess readhesion properties, so that the sheets adhered to an adherend by applying said solid adhesives can not be removed from the adherend without damaging the sheets or adherend. Accordingly, once the sheets are peeled off from the adherend, readhesion can not be attained.
Stick adhesives which enable articles to be removably bonded to substrates have been disclosed by Gollub et at in the U.S. Pat. No. 4,716,189. An aqueous dispersion of polyethylene ethyl is employed for attaining said purpose. Said stick adhesives would be helpful for temporarilly adhereing the sheets to an adherend in such a condition that the sheets can be removed from the adherend later. The sheets thus removed from the adherend, however, would not be able to be adhered again to the adherend. Namely, consecutive cyclic usage of adhesion-removal-readhesion would not be able to be attained by said stick adhesives.
On the other hand, blends of polymers including a tackifying resin have been disclosed in the U.S. Pat. No. 4,367,113, which have good adhesion to a number of materials and are suitable for use in the manufacture of laminated sheet constructions as well as for employment as hot melt adhesives. For example, the powdered blend of polymers are distributed over one sheet of polyester film and a second sheet of polyester film is laid on the assembly. Then the assembly is subjected to heat and pressure to obtain a laminated structure of two sheets which are adhered strongly to each other. Removability and readhesion, however, can not be obtained. Stick adhesives gelatinized by a gel-forming agent which can be used in the same manner as in the conventional solid adhesives have not been obtained.